Concorde, these numbers don't add up to the formula. Either you have low pro tires or 3.58 roughly rear ratio ? Any thoughts ? With the configuration that you have you should be at 1275rpm at 65 mph ?? Am I doing something wrong with my calculations ??
Our trucks our governed at 65, they turned the RPMs down to where it runs 65 at 11-1200 RPMs max. It didn't effect the power in my mind, but Volvos actually pull very well even when governed. I am getting 7.7 miles per gallon as of today, my load is 39000 roughly in a slightly heavier reefer trailer. If you run 65 mph at 1400 RPMs, the sweet spot on that particular truck has to be somewhere around 60-63 mph if you're trying to get good fuel mileage. More RPMs means more power, more fuel consumption, especially under heavy loads.
My opinion is the 3.70s are a great all around gear esp if running a lot of hill country. Looking at that chart if you stay 63-65 you're looking at good overall mpg and better start-ability than the taller rears